Circular lapping machine



May 7, 1963 W. G. MUSHRUSH CIRCULAR LAPPING MACHINE Original Filed Feb.1, 1955 3 Sheets-Sheet l IN VEN TOR. W/Lso/v GEORGEMUSHRUS H A TTOENE YMay 7, 1963 w. G. MUSHRUSH CIRCULAR LAPPING MACHINE Original Filed Feb.1, 1955 5 Sheets-Sheet 2 Fig. 3

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May 7, 1963 w. G. MUSHRUSH CIRCULAR LAPPING MACHINE Original Filed Feb.1, 1955 3 Sheets-Sheet 3 INVENTOR. WILsONGmRGE MUS/ RUSH Q ZA ZM 4Trot/45v nite This invention relates generally to the art of abradingand more particularly to an apparatus for lapping or polishing objects.

This invention is a division of application Serial No. 485,494 filedFebruary 1, 1955, for Circular Lapping Machine, now United States PatentNo. 2,922,264 dated January 26, 1960.

The principal object of this invention is the provision of an apparatusfor polishing or lapping end surfaces on articles. The motion creatingthe abrading-lapping action is a vibratory reciprocatory motor-drivenmovement of a lapping plate in an inclined arcuate path about a verticalcentral axis effective to convey the parts to be lapped over and incontact with the abrading surface of the plate. The movement of theabrading surface contacting the parts to be lapped is provided by amotor adapted to produce such motion, preferably, as illustrated in thisapplication, an electromagnetic motor, such, for example, as thatillustrated and described in Weyandt Patent No. 2.658,609 is used.

The frequency and amplitude of reciprocal arcuate movements caused bysuch a motor is governed by the frequency of the alternating current andthe power input energizing the motor. Ordinarily the frequency of suchcurrents, as almost universally available for normal power purposes, is60 cycles per second. However, the effective reciprocating movement ofthe plate produced by such current may, by suitable control, produce adriving reciprocatory motion at a frequency one half, the same as, ordouble that of the alternating current frequency, or at a slightly lessor greater frequency than that of the current, by use of controls knownto the vibratory motor art. This produces a rapidly reciprocatingvibratory movement of a circular lapping plate driven by the motor inforward and back and up and down directions. The reciprocating movementof any point on the circular plate differs in amplitude and path ofarcuate movement from any other point on the circular driven plateaccording to distance of the respective points from the axis of thedriven plate. The amplitude can be adjusted to work requirements bymeans well known in the vibratory motor art.

With specific reference to the circular or arcuate lapping or polishingmotion, it has been discovered that this action coupled with arelatively small diameter flat abrading surface, produces a novel actionin lapping an article when the dimension of which is less than half thedimension of the diameter of the flat abrading surface. When such asurface is vibrated in an inclined arcuate path of motion about itscentral axis, the center of the surface has a materially less arcuatemovement than that of the perimeter. Since the article has a width, thewhole area which is simultaneously acted upon by the vibrating surface,onehalf of the article is being vibrated through a smaller me than theother half. In fact, the arcuate movement varies in magnitude from zeroat the center of the vibrating surface to a maximum at its periphery.Thus the article will rotate about its own axis as it moves forward andthis rotation will always be toward the center or the smaller arc ofvibration. This movement of the lapping surface with which the articlebeing lapped is in contact produces a rotary motion of the article aboutits own axis and simultates atent taneous movement of the article aroundthe axis of the plate. If the body is as large as the vibrated surface,it will, of course, rotate about its own axis which would be the sameaxis as that of the vibrating surface. By the continuous rotating andsimultaneous revolving movement of articles on the lapping surface bythe apparatus here disclosed the abrading action is applied to the facebeing lapped in constantly changing directions. This results in a smoothlapped surface without scratches or unequal reduction of the surface, asmay result from grind ing or manual polishing.

Another advantage and object of this invention is the ability of lappingopposite surfaces simultaneously. The articles being polished or lappedmay be positioned on the vibrating surface and a weight having a similarsurface supported on top of the articles. This weight having a similargrinding surface will polish or lap the top of the articles as thisinclined arcuate vibratory path of vibration must be transmitted throughthe articles onto the weight, which being substantially as large as thevibratory disc will merely rotate but not as fast as the articlesthereunder and in contact therewith.

In the apparatus illustrated and described, a circular plate having ineffect an abrasive surface and a peripheral bounding flange or wall forretaining parts being lapped, and retaining lapping slurry, is driven bythe vibratory motor. In effect, this forms a circular bowl provided witha bottom plate provided with a lapping surface. The walls will retainthe lapping material Whether it be liquid, powder suspended in a liquid,or merely a powder. This material may be combined with cloth or paperabrasive secured to the vibrating plate and weight. Such surfaces mayalso be covered with non-abrasive cloths or coverings such as cork,felt, or flannel employed with or without rouge. Each of these featuresprovide a novel improvement in the art.

The lapping plate forming the bottom of the bowl by which articleshaving a plane surface are to be lapped will be flat. If the surface isdished or spherical, then a similar surface is lapped on the articles.

Another object is the provision of vibratory lapping with variedpressure against the article and the abrading surface. This variablelapping pressure controls the fineness of the lapped surface.

Another advantage of a circular electro-magnetic lapping machine of thischaracter is that it can be allowed to continue with little or noattention without fear of spoiling the tool, machine, or article.

Other objects and advantages appear following description and claims.

The accompanying drawings show for the purpose of exemplificationwithout limiting the invention or claims thereto certain practicalembodiments illustrating the principles of this invention wherein:

FIG. 1 is a view in vertical section of the lapping machine. 1

FIG. 2 is a top plan view with the pressure plate removed.

FIG. 3 is a view in section of a dished pan with a smooth spherical gritsupporting surface and a fiat cloth covered pressure plate.

FIG. 4 is a view in section of the pan secured thereto and a pressureplate having a cork surface.

FIG. 5 is a view in section showing the lapping machine having a fluidpressure plate capable of varying the pressure of the article on thelapping surface.

FIG. 6 is a perspective view of a turning guide and bridge on thelapping bowl.

FIG. 7 is a modified turning guide on the lapping bowl.

Referring to the drawings, the motor employed to illustrate theprinciples of this lapping and polishing machine is that of anelectromagnetic motor which comprises the hereinafter in the base 1preferably a massive structure supported by resilient feet 2 and carriesan outer casing 3 which encloses the motor.

The base 1 is provided with a plurality of sloping seats 4 symmetricallydisposed about a vertical central axis indicated by a construction line5. As shown the seats 4 support the lower ends of the tuned cantileversprings 6 of which there are four sets symmetrically disposed with oneon each side of the base. The upper ends of these leaf springs aresecured to the corresponding seats 7 formed on the frame structure 8.This frame member is provided with openings to receive the mountingbolts 19 for securing the polishing plate 11 to the frame.

The motor illustrated is of the electromagnetic type and comprises acore member 12 which is E-sha ed and which is adjustably mounted on thebracket 13 on top of the base 1 by means of the mounting bolts 14. Thecenter post of the core 12 is provided with an electromagnetic coil 15and its electrical connections extend to the operating controls. Byproperly mounting the core 12 on the base, its pole faces will besymmetrically mounted relative to the armature 16 which in turn issecured to the under side of the frame 8. The armature 3.6 is centrallymounted relative to the axis and the springs which support the framealso position the armature 16 relative to the pole faces of the core 12so as to provide a proper air gap between the armature 16 and each ofthe pole faces of the E-shaped core. By energizing the electromagneticcoil 15 with current impulses, the electromagnetic energy impulses ofthe core draw the armature down causing the springs 6 to hex and movethe frame in a helical or an inclined arc'uate path of movement. Whenthe energ impulse passes, the springs return to their normal positionpermitting the frame to rise again to its normal position. The springstravel slightly beyond the stationary position, thus providing acomplete oscillatory movement in an inclined arcuate path. The movementsof the lapping plate above described in this paragraph are all relativeto a'fixed vertical axis normal to the circular flat lapping surface.

By tuning the springs 6 to reciprocate the frame at a frequency of a fewcycles more or less than the frequency of the driving energy impulses,the vibratory system would follow in synchronism with the frequency ofthe energy impulses and the best operation of this reciprocatingvibratory device will be obtained. Such vibratory motors produce a rapidreciprocatory movement of the lapping base upon which the articles beingtreated rest.

If the armature is made of permanent magnet material the frame willreciprocate in synchronism with the energy impulses such 'as anysuitable source of alternating current since one impulse would attractthe armature and the next impulse would repel the armature. If thearmature is made of laminated steel, the field would be reciprocated atthe rate equal to twice the frequency of the alternating current, aseach cycle has two current impulses.

A half-wave rectifier such as shown at 17 can be employed to reduce thenumber of alternating current impulses to that of the frequency of thecurrent. The armature and the parts attached thereto are attracted byeach alternate current impulse to reciprocate at the frequency of thealternating current.

The magnitude of the current impulses is controlled by a simple rheostatas shown at 18. The coil 15 of the halfwave rectifier 17 and therheostat 18 are all connected in series across the source of alternatingcurrent.

As illustrated in the drawings the polishing plate 11 is in the form ofa bowl having a uniform flat bottom 20 and an annular retaining flangeor wall 21. The grinding surface is provided with a grinding cloth orsimilar material such as illustrated at 22. The articles being ground'are the rings 23 which have their small bearing surface facing on thecloth 22 and their larger bearing surfaces inengagement with the corksurface 24 of the pressure plate 25. Boththe cloth surface 22 and thecork surface 24 are cemented or otherwise secured to the grindingsurface 2tl of the bowl 11 and to the under surface of the pressureplate 25 respectively. The pressure plate 25 is also provided with ahandle 26 to lift the same out of thebowl. It will be noted that thepressure plate has considerable body to provide it with suh'icientweight needed for lapping pressure on the article between the cork 24and the cloth grinding surface 22.

The bowl 11 and its lapping plate bottom as shown in FIG. 2 is circularand the articles 23 rotate on their respective axes and incounter-clockwise direction as the articles themselves revolve aroundthe axis of the bowl within the bounding peripheral flange. The pressureplate 25 is likewise round and has a small clearance as indicated at 27between its lower edge and the wall 21 of the bowl 11. However, thesides of the pressure plate 25 are beveled as indicated at 28 so as tominimize friction between the plate and the walls 21. When liquidabrasives are used the plate reduces splashing. The rapidity of thelapping action is dependent to some extent on the pressure between theabrasive surface and the face being treated. Usually the articles areweighted to increase the speed of lapping action. For articles havingsubstantial intrinsic weight, as for example, steel parts and the like,the weight of the articles themselves may be sufhcient to secure desiredlapping results. The time required will vary to some extent in inverseproportion to the pressure per unit of surface contact of the articleson the lapping member.

The abrasive cloth 22 may be an emery cloth, a Carborundum cloth or acrocus cloth. However, loose abrasive powders of these materials andGamma Alumiira, Linde B, which is sapphire dust, or cerium oxide may beemployed. When employing a powder like Gamma Alumina', it is usuallyprovided in a water solution. In place of the abrasive cloth 22 one mayemploy a pad such as a Buehler brand microcloth or red felt. Buehlerbrand red felt is ordinarily employed with Gamma Alumina. It

may also be used with a Linde B abrasive. Microcloth' is a cotton fabricdisc filled with rayon fibers.

If opposite sides of the article are to be lapped the abrasive cloth 22is on the 'bowl bottom and the abrasive cloth 24 is mounted on thepressure plate with the article therebetween and thus both sides arelapped simultaneously. The article may be turned upside down to insureasmooth and uniform lapping surface. In order to insure non-rotarymovement of the pressure plate when it is desired to lap the uppersurface, a bar such as indicated at 3th is extended through the handle26 and engages the upwardly open notches 29 in the bowl rim whichprevents the pressure plate from rotating. However, the pressure platewill retain its full pressure on the lapped articles as they arebeinglapped. Other lubricants commonly used with the powders are turpentine,water, kerosene, lard and machine oil. Kerosene is generally employedwith the cloth, and water for abrasive powder. If the articles beinglapped are heavy they need no pressure plate as their own weight willbe'sufficient.

As illustrated in FIG. 3, the bowl 31 is provided with a sphericalbottom surface the bottom of the ring 33. The pressure plate 34 is similar to the pressure plate 25 and it is provided with a handle 35 but itis also provided with a central magnet-36 which co-acts with the magnet37 in the bottom of the bowl for the taining the pressure mately so.

plate in its center position or approx} A slight movement of thepressure plate laterally is permitted and will not produce inaccuracy as32 for the purpose of lapping purpose of increasing the pressure and re-As shown in FIG. 4 the bottom of the bowl 11 has a grinding surface 20which is merely a cast iron grinding surface and the pressure plate 40is provided with a series of weights 41, 42 and 43. Thus by adding orsubtracting these weights on the pressure plate, one may add or subtractthe pressure on the grinding surface between the articles 23 and thegrinding surface 20. A cork surface 24 is placed on the under side ofthe pressure plate 49.

As shown in FIG. the grinding bowl 11 is provided with a grindingsurface 21) and the pressure plate 50 has mounted thereon a second plate51 which is supported thereon by an annular antifrictional bearingstructure 52. A fence or guard 53 encloses the plate 51 and protects thebearing structure which rides in the race common to both the plates 50and 51. Between the plate 51 and the bridge member 54 is a fluidpressure device 55 which when supplied with fluid under pressure expandsor contracts and thus adds more or less additional pressure on thepressure weight 5% This in turn is effective on the parts 23. However,in addition to the pressure device 55 one can employ a spring 56 whichis loaded by the device 55. Thus the spring, not being capable offollowing the vibratory movement of the electromagnetic motor, permitsthe pressure plate 5% to rotate. However, the pressure plate 51 and thefluid actuating device 55 and the springs 56 remain stationary :beingconnected with the bridge 54. In this manner one can vary the lappingpressure during the operation of the device.

When lapping optical fiats, or other articles which require it, andspeedier and more proficient lapping action is desired, a turning guideand bridge such as shown in FIGS. 6 and 7 may be employed. As shown inFIG. 6 a bridge 69 is extended over the top of the bowl 21 and isequipped with depending fingers 61 and 62 which frictionally engage thepressure plate 63 at a point 64, and by friction resulting the uppersurface of the pressure plate is given an added twist as it revolvesaround the bowl. The pressure plate 63 revolves to a point beyond whichthe fingers no longer contact the friction point thereby releasing thepressure plate for travel in the bowl to the second finger 62 where thesame operation is repeated. 1

In FIG. 7 the bridge 60 on the bowl 21 has the guide 65. The pressureplate 66 is equipped with a series of fingers 67 which engage the guidethereby obtaining an added twist and speed to the normal rotation of thepressure plate and thereby increases the lapping action.

I claim:

1. A lapping machine comprising a lapping surface means includingabrasive particles for receiving thereon the surface of at least onearticle to be lapped, resilient means to support said lapping surfacemeans facing upwardly and for movement as a free body in an inclinedarcuate path of movement about a vertical central axis that is disposedsubstantially normal to the surface to be lapped, and a motor means todrive the lapping surface means in said inclined arcuate path ofmovement.

2. The structure of claim 1 which also includes an abrading surfacesecured to said lapping surface means.

3. The structure of claim 1 which also includes a wall surrounding saidlapping surface means to retain a loose lapping material and a liquidthereon.

4. The structure of claim 3 which also includes a pressure plate havingan underside to rest on the article to add weight on the surface beinglapped.

5. The structure of claim 4 which also includes a beveled edge on theperimeter of said pressure plate to decrease the area of the pressureplate edge that occasionally engages said wall.

6. The structure of claim 4 which also includes a lapping surface meanson the under side of said pressure plate.

7. The structure of claim 4 which also includes a cork surface on theunder side of said pressure plate.

8. The structure of claim 4 which also includes means to exertadditional pressure on the pressure plate.

9. The structure of claim 8 characterized in that said means includesweights added to said pressure plate.

10. The structure of claim 8 characterized in that said means includes abridge attached to said motor and fluid pressure means acting betweensaid bridge and pressure plate to vary the pressure thereon.

11. The structure of claim 1 characterized in that said lapping surfacemeans is dished.

12. A lapping machine comprising a base reaction member, a frame havinga lapping surface means including abrasive particles, an upstandingannular wall on said frame to retain articles having a surface to belapped, a plurality of tuned resilient means to support said frame andlapping surface means facing upwardly and for movement as a free body inan inclined arcuate path about a vertical central axis, motor means toapply to said frame spaced impulses to reciprocate said frame andlapping surface means along said arcuate path of movement, and means toprovide relative movement between surface being lapped and said lappingsurface means laterally of said arcuate path.

13. A lapping machine comprising a base reaction member, a frame havinga lapping surface means including abrasive particles, an upstandingannular wall on said frame to retain articles having a surface to belapped, a plurality of tuned resilient means to support said frame andlapping surface means facing upwardly and for movement as a free body inan inclined arcuate path of movement about a vertical central axis,motor means to apply to said frame spaced impulses to reciprocate saidlapping surface means along said arcuate path of movement.

14. A lapping machine comprising a base reaction member, a frame, a bowlmounted on said frame and having a fiat bottom lapping surface meansbounded by an upstanding wall to hold a liquid lapping compound andretain an article having 'a surface to be lapped, and motor means toapply a feeding action to said bowl to move the surface of the articlein engagement with the liquid lapping compound.

15. A lapping machine, consisting of a lapping plate having a lappingsurface means including abrasive particles for freely supporting anarticle, an upstanding annular wall on said lapping plate to retain thefreely supported articles, means to support said plate with said lappingsurface means facing upwardly and guided for reciprocation in an arcuatepath inclined relative to said lapping surface means, and motor means toreciprocate said lapping plate in its guided arcuate path to move thearticle over said lapping surface means.

16. Apparatus according to claim 15 including a pressure plate to restand add pressure on the article while it moves over said lapping surfacemeans of said lapping plate.

17. Apparatus according to claim 16, characterized by the fact that thepressure exerted by the article on the lapping plate during the lappingoperation is variable.

18. Apparatus according to claim 15, characterized in that said meansfor supporting said lapping plate includes flexible members disposedsymmetrically about a vertical central axis of said plate and inclinedrelative to the lapping surface thereof, said plate being reciprocatedin an arcuate path about said axis by said motor means.

References Cited in the file of this patent UNITED STATES PATENTS2,114,966 Myers Apr. 19, 1938 2,585,637 Dremel Feb. 12, 1952. 2,658,609Weyandt Nov. 10, 1953 2,700,259 Dreyfus Jan. 25, 1955

1. A LAPPING MACHINE COMPRISING A LAPPING SURFACE MEANS INCLUDINGABRASIVE PARTICLES FOR RECEIVING THEREON THE SURFACE OF AT LEAST ONEARTICLE TO BE LAPPED, RESILIENT MEANS TO SUPPORT SAID LAPPING SURFACEMEANS FACING UPWARDLY AND FOR MOVEMENT AS A FREE BODY IN AN INCLINEDARCUATE PATH OF MOVEMENT ABOUT A VERTICAL CENTRAL AXIS THAT IS DISPOSEDSUBSTANTIALLY NORMAL TO THE SURFACE TO BE LAPPED, AND A MOTOR MEANS TODRIVE THE LAPPING SURFACE MEANS IN SAID INCLINED ARCUATE PATH OFMOVEMENT.